The Beddington Zero Energy Development, in London, makes full use of the valuable south facade for passive heating as well as photovoltaics.

Figure 2: A Trombe Wall allows heat collection
without light to minimize glare and color fading
and to delay the solar heating from day to night.
The surface of the wall facing the glazing should
be as dark as possible, with black or a high-tech
selective coating being best. The glazing need not
be transparent and is often translucent instead. A
mixture of direct gain (windows) and Trombe wall
usually is best.

Figure 3: In many climates, it is still cold on March
21 and still hot on Sept. 21. Since the altitude
angle of the sun is the same on those two days,
a fixed overhang, obviously, cannot fully shade
a window on Sept. 21 and allow complete sun
access on March 21. All temperate climates have
the same problem because of the mass of the
Earth, which creates a time lag; the thermal year
and solar year are out-of-phase. Only a movable
shading device, like an awning, will give the high
performance needed today.